The present invention concerns a process for treating and imparting value to sulfuric sludges of petroleum origin which essentially consists of reacting said sludges on urea in defined proportions in such a way as to involve the sulfuric acid in a particular sulfuric acid urea complex composition. It also concerns the composition resulting from said process. The process makes it possible to recover sulfuric acid in order to impart value thereto as well as a part of the organic compounds present in the sludges.
The prior art is illustrated in particular by U.S. Pat. No. 4,397,675 and by the article Chem. Abstracts, Vol 113, No 18, 29th October 1990, Columbus, Ohio, U.S.; Abstract No 155 239 k, page 166.
It is known that certain chemical operations, in particular those which are effected in alkylation procedures, and in particular aliphatic alkylation procedures, are carried out in the presence of concentrated sulfuric acid which performs a catalysis function. Unfortunately a part of the acid involved occurs at the end of the operation in the form of impure sulfuric sludges, the elimination of which gives rise to many problems. The present invention makes it possible in particular to treat and impart value to such sludges which result from aliphatic alkylation reactions.
The man skilled in the art knows that the essential part of such sludges is formed by mixtures or complex combinations as between sulfuric acid and certain organic residues. Their mean composition by weight fluctuates between the following values, expressed as a percentage by weight:
H.sub.2 SO.sub.4 88 to 96% PA1 H.sub.2 O 2 to 6% PA1 organic residues 2 to 6%.
The applicants found that treatment of such sludges by means of urea in a defined proportion could give rise to compositions which can be put to valuable use while a part of the organic residues, for example in the form of hydrocarbons, could also be recovered.
It is known to obtain, as between urea and sulfuric acid, mono- and bi-urea complexes with well-defined melting points. It is also known that the complexes, as between themselves and with urea, give compounds which are fusible at low temperature. Thus a eutectic comprising 3.6 moles of urea for one mole of sulfuric acid occurs in the form of a liquid which is stable at a temperature close to 25.degree. C.